I used my pruning shears as a point of reference. You can see that the root of this dandelion is as thick as the handles of the pruning shears.
This dandelion wasn't blooming at the moment, but normally the stems get up to two feet tall and have multiple blooms. They grow insanely quickly too, which is why I mow them down every week or so.
For those of you who think photos of pets are cute, here's one of my "baby" -- or at least, who was my baby before I had my baby. ;o)